Once you've passed the selection they won't tell you what fleet you'll be put on, reason being they don't know themselves.
To be eligible for the A330 you must have widebody experience, or at least this is the latest news I have. The A320 fleet will eventually be phased out, because the plane is too small even for their short routes.
If you pass the selection you will be put in the holding pool and when sim slots come up they will offer you a contract on a specific aircraft. The current trend is that they are finding plenty of A300 rated guys and most new non type rated guys are going on the A320 fleet and moving A320 and A300 guys from those fleets to the A330. After 18 months on the A320 you can expect to move onto the A330/340. However, this could all change in a few months time.